A new diagnostic procedure for CADUCEUS has been developed, which we believe provides a framework for solving all of the known problems encountered in our use of INTERNIST-1. During the five year period covered by the current proposal, we intend to pursue the following specific aims: Revision of the structure of the CADUCEUS knowledge base will be undertaken to support the enhanced capabilities of the new diagnostic procedure. The revised knowledge base will be expanded to encompass all of the major diseases of internal medicine, and much of neurology. Evaluation of the new CADUCEUS system will be undertaken in two phases. First, through protocol analytic studies, we intend to study and refine the human/machine interface of CADUCEUS, exploring specifically various modes of cooperative human/machine problem solving. Subsequently, we plan to carry out formal evaluation studies of the system in order to gauge its diagnostic accuracy, the value of its information gathering and explanatory capability, and its acceptability to a variety of potential client groups. The overall objective for this five year effort will be to bring CADUCEUS to a state of maturity that will permit its distribution for general use by medical practitioners.